Few things are better at conveying what a nation really cares than how it spends its money. On that measure, Americans like to punish.

The United States spent about $80 billion on its system of jails and prisons in 2010 — about $260 for every resident of the nation. By contrast, its budget for food stamps was $227 a person.

In 2012, 2.2 million Americans were in jail or prison, a larger share of the population than in any other country; and that is about five times the average for fellow industrialized nations in the Organization for Economic Cooperation and Development.

The nation’s unique strategy on crime underscores the distinct path followed by American social and economic institutions compared with the rest of the industrialized world.

Scholars don’t have a great handle on why crime fighting in the United States veered so decidedly toward mass incarceration. But the pivotal moment seems to have occurred four decades ago.

“With few and isolated exceptions, the rehabilitative efforts that have been reported so far have had no appreciable effect on recidivism,” he wrote. Standard rehabilitation strategies, he suggested, “cannot overcome, or even appreciably reduce, the powerful tendency for offenders to continue in criminal behavior.”

Crime was rising in the 1960s and 1970s, alarming the public and increasing the risk to politicians of appearing “soft” on crime.

The decline in manufacturing employment, once the backbone of many urban economies, wasn’t helping. Later, in the 1980s and ’90s, crack cocaine became a scourge of the nation’s inner cities.

But as Steven Raphael of the University of California, Berkeley, and Michael A. Stoll of the University of California, Los Angeles, note in their book “Why Are So Many Americans in Prison?,” what drove up imprisonment rates was not crime but policy.

If rehabilitation was out of reach, the thinking went, all that was left was to remove criminals from society and, through harsh sentencing, deter future crime. From 1975 through 2002, all 50 states adopted mandatory sentencing laws, specifying minimum sentences. Many also adopted “three strikes” laws to punish recidivists. Judges lost the power to offer shorter sentences.

And the prison population surged. Four decades ago, the correctional population in the United States was not that dissimilar from the rest of the developed world. Less than 0.2 percent of the American population was in a correctional institution. By 2012, however, the share of Americans behind bars of one sort or another had more than tripled to 0.7 percent.

Bruce Western of Harvard suggests a specific American motivation, which sprang to some degree from the victories of the civil rights movement.

“The crime debate was racialized to an important degree,” Professor Western told me. “The anxieties white voters felt were not just about crime but about fundamental social changes going on in American society.”

Today, a little under half the state and federal prison population is black. The Bureau of Justice Statistics estimates that a black boy born in 2001 had a 32.2 percent chance of doing time behind bars.

Growing inequality, too, appears to have played a role. As Devah Pager of Harvard told me: “There is something to the idea that the more distant the rich become to the poor, the easier it is to impose policies that are more punitive than others.”

Professor Raphael is wary of linking incarceration with income dynamics. Still, he agrees the trends are suspiciously similar. “In the 1970s, something changes,” he told me. “The increasing concentration of income at the top follows the incarceration rate almost perfectly.”

The United States had another singularity: a comparatively small welfare state that struggled to address social and economic dislocation. “The criminal justice system became the only effective institution that could bring order and manage urban communities,” Professor Pager said.

Prison, according to Professor Western, “became a last resort for a whole variety of social failures.” Whether it is caused by problems with mental health, drug abuse or unemployment, he said, “all the people that slip through the safety net and end up in crime end up in the prison system.”

What did we get from this? Crime rates have fallen by almost half since 1990, to the lowest level since the early 1970s. But that may have little to do with mass incarceration. Demographic trends — there are simply fewer young men around — help explain much of the decline. Some states, like New York, have managed to reduce crime even while cutting the prison population through better policing.

The United States still suffers higher rates of violent crimes than European countries that have lighter sentencing policies. In 2012, the United States had five intentional homicides for each 100,000 people. In Canada, the rate was 1.8. In Australia, 1.2. Mass imprisonment not only suffers from diminishing returns. After a certain point, it might actually increase crime.

Indeed, a growing body of research has concluded that the costs of the strategy are much steeper than prisoners’ room and board.

Anna Aizer of Brown University and Joseph J. Doyle Jr. of the Massachusetts Institute of Technology found that putting a minor in juvenile detention reduced his likelihood of graduating from high school by 13 percentage points and increased his odds of being incarcerated as an adult by 23 percentage points.

The impact of incarceration on a former inmate’s future life is difficult to disentangle. Still, a report by Mr. Western and Becky Pettit of the University of Washington suggested that serving time reduced men’s hourly wage by 11 percent and annual employment by nine weeks.

More than half of inmates have minor children. Their children are almost six times as likely to be expelled or suspended from school. Family incomes fall 22 percent during the years fathers are incarcerated.

California — which had to release tens of thousands of prisoners in 2011 and 2012 to reduce prison crowding — offers a perspective into what life might be with a more lenient approach.

According to calculations by Professors Raphael and Stoll, there were 1.2 more auto thefts for every prison year not served. Violent crime wasn’t affected at all.

Extrapolating to a national scale, they estimated that reducing the imprisonment rate by 20 percent would lead to 121 new property crimes for every 100,000 Americans, a 5 percent increase over 2012.

This is a price American voters, and their elected officials, might be willing to pay — especially if they can save money on prisons.

Even Southern states that traditionally locked up criminals for as long as possible, like Georgia and Kentucky, have begun to experiment with cheaper, less punitive alternatives.

In Washington, a bipartisan group of senators — as varied as the Texas Republican Ted Cruz on the right to Patrick Leahy, the Vermont Democrat, on the left — are supporting a bill to lighten sentences for low-risk drug offenders.

These changes could turn around the imprisonment juggernaut. After rising relentlessly for three decades, the nation’s incarceration rate hit a peak in 2008 and started gradually to decline. In 2011 and 2012, the total correctional population actually shrank slightly.

We might spend the savings on food stamps.

Email: eporter@nytimes.com;
Twitter: @portereduardo

A version of this article appears in print on , on Page B1 of the New York edition with the headline: In the U.S., Punishment Comes Before the Crimes. Order Reprints | Today’s Paper | Subscribe